Oh Tan, that must be so frustrating I can relate as my nearly 5 yo is in a similar boat although not to the same extent and thankfully not the smearing.

We have found the greatest improvement has come from seeing an OT for this. She has been absolutely fantastic, and while I think it's too soon to say that all is well, things are certainly better than they were. Have you been working with an OT at all? If not, maybe that's something to think about, and if so, maybe you could ask the advice of the OT as to what to do. I am constantly amazed at the number of strategies they seem to have!

I hope you find some answers hun. It really is hard to deal with.